The device and method disclosed in this document relates to battery disconnection units and, more particularly, to a smart contactor for a battery disconnection unit.
In high-voltage battery powered systems, such as those of electric and hybrid-electric vehicles, very stringent requirements are placed with respect of reliability, safety, power-carrying capacity and service life. A common requirement is that such systems have a mechanism for emergency shut-off. Emergency shut-off may be required, for example, in the event of system-related faults (short circuit) or in the event of accidents. Prompt disconnection of the battery is often required to prevent fires in the vehicle or damage to the battery in the event of an accident or a short circuit.
Some systems employ a battery disconnection unit that disconnects the battery from the vehicle power system so as to interrupt the flow of current from the battery in the event of an accident or short circuit. A battery system 100 having an exemplary battery disconnection unit (BDU) 104 is shown in FIG. 1. The battery system 100 includes a battery pack 108 having a positive terminal 112 and a negative terminal 116. The battery disconnection unit 104 is connected between the battery pack 108 and the vehicle power system (not shown) and is configured to selectively disconnect the battery pack 108 from the vehicle power system in response to control signals from a battery control unit (BCU) 120.
The battery disconnection unit 104 comprises a high-side contactor 124 and a low-side contactor 128. The high-side contactor 124 is connected between the positive terminal 112 of the battery pack 108 and a positive connector 132 to a positive power line or rail of the vehicle power system. The low-side contactor 128 is connected between the negative terminal 116 of the battery pack 108 and a negative connector 136 to a negative power line or rail of the vehicle power system. The battery control unit 120 is configured to operate the high-side contactor 124 with a high-side control signal 140 to selectively open and close the high-side contactor 124. Similarly, the battery control unit 120 is configured to operate the low-side contactor 128 with a low-side control signal 144 to selectively open and close the low-side contactor 128. In this way, the battery disconnection unit 104 enables disconnection of the battery pack 108 in response to commands from battery control unit 120.
In some circumstances, such as in the event of an accident, a short circuit may be established between the positive and negative power lines of the vehicle power system. If the battery pack 108 remains connected the vehicle power system in such a scenario, substantial current flows from the battery, which generates substantial heat that will not only cause damage to the battery, but potentially cause a fire in the vehicle. To protect against dangerous over-current situations, the battery disconnection unit 104 further includes an oversized fuse 148 connected in series with the high-side contactor 124 and configured to blow in an over-current situation, thereby interrupting the flow of current from the battery pack 108 to the vehicle power system.
Due to the high voltages and currents of the power system 100, the fuse 148 must be very large. Additionally, the fuse 148 must be large to prevent from blowing due to aging (degradation). Among other things, this oversizing of the fuse 148 contributes to increased reaction times for the fuse 148 to blow in an over-current situation. While expected fuse reaction times is still on the order of milliseconds, in the presence of a short circuit, currents can nevertheless increase to over a thousand amps before the fuse actually breaks the over-current. Accordingly, there is a high probability of catastrophic damage to the battery pack 108.
What is needed is a reliable mechanism for prompt disconnection of a battery pack in an over-current situation, which is substantially faster than a traditional battery disconnection unit having oversized fuse. It would also be advantageous if such a mechanism does not increase the complexity of the battery disconnection unit and, preferably, reduces the total parts count for the battery disconnection unit.